1. Field Of The Invention
This invention relates to fluid driven dental handpieces, particularly of the straight type.
2. Description Of The Prior Art
Modern dental handpieces of the above type generally comprise a chuck or collet which is powered by an air driven motor located in the handpiece itself. Turbine motors are not generally satisfactory for straight type handpieces as they operate most efficiently at high speeds, on the order of 250,000 rpm or more, and have relatively low torque. The speed of the turbine can be reduced by throttling the supply of air applied thereto under pressure but in doing so, the torque is further reduced.
For certain types of dental work, it is often desirable to operate a handpiece at relatively lower speeds and at higher torque. For example, it has been found that certain tooth cleaning, drilling and other operations are best performed at speeds on the order of 5,000 rpm whereas certain polishing operations are better performed at somewhat higher speeds, on the order of 15,000 to 25,000 rpm. Vane type air driven motors with gear reduction have been used heretofore in order to obtain such lower speeds and higher torque. However, here also, reduction in speed, as required for certain types of dental operations, is generally accomplished by throttling the air supply which tends to reduce the torque of the motor. Further, the vanes in such vane type motors tend to stick in retracted positions in their rotor slots due to accumulation of foreign matter therein. Such foreign matter is partly derived from products of internal motor wear. Such sticking results in erratic motor start-up, requires excessive air pressure and generates unpredictable break-away speeds.
Accordingly, a principal object of the present invention is to provide a compact dental handpiece or the like including an air motor and a readily adjustable change speed transmission means intermediate the motor and the chuck.
Another object is to facilitate selection of different drive ratios in a speed transmission means in a dental handpiece or the like.
Another object is to provide a simple and compact chuck for a dental handpiece or the like which is readily adjustable between open and closed conditions.
Another object is to reduce sticking of vanes in retracted positions in the slots of a vane type air motor for dental handpieces or the like.
Another object is to enable a swivel action between the finger grip area of a forward barrel and a rear barrel to nulify a build-up of torsional forces in the flexible conduits between the handpiece and the source of air under pressure.
Another object is to eliminate the need for periodic lubrication of the operating parts.
Another object is to facilitate dismantling of a dental handpiece of the above type.